Neurorehabilitation in Patients With Disorders of Consciousness: Multidimensional Ambispective Study on the Impact of Single and Combined Approaches

The protocol is grounded in the increasing survival of patients with severe acquired brain injury due to advances in intensive care, which has led to a growing population with prolonged DOC and substantial socio-economic burden, including lifetime care costs exceeding one million euros in some estimates. Within this context, neurorehabilitation is conceptualized as a multidimensional process targeting arousal, awareness, motor and cognitive function, communication, and autonomy, and the study posits that combining structured sensory stimulation with non-invasive brain stimulation and technologically assisted communication can enhance residual brain plasticity and functional recovery beyond that achieved with standard conservative approaches. The rationale emphasizes that DOC assessment based solely on overt behavioural responses is vulnerable to misclassification, underscoring the importance of integrating advanced neurophysiological, neuroimaging, and biological markers to more accurately quantify residual consciousness and track treatment-related changes.

From an intervention standpoint, the protocol details a spectrum of non-invasive treatments: multimodal SS consists of repeated, simple, emotionally salient, or autobiographical stimuli delivered through auditory, visual, tactile, and olfactory channels, which can be administered singly or in combination to enhance arousal and behavioural responsiveness. AAC systems with eye-tracking enable "active" sensory stimulation by pairing visual and auditory stimuli with graded tasks whose performance is inferred from oculomotor behaviour, thus offering both diagnostic information about cognitive abilities and opportunities for structured engagement with the environment. tDCS is introduced as a low-intensity direct current technique applied repeatedly to modulate resting-state membrane polarization and network connectivity, with advantages over repetitive TMS in terms of safety, logistical simplicity, and potential for inducing longer-lasting neuromodulatory effects; TMS is framed as a complementary, focal method of electromagnetic stimulation targeting cortical regions relevant for consciousness.

The protocol allocates substantial attention to biomarkers and mechanistic readouts, particularly the role of neurofilament proteins as indicators of axonal integrity and neuroaxonal damage. Neurofilament light chain (NfL), owing to its relative specificity compared with traditional markers such as neuron-specific enolase, S-100B, and glial fibrillary acidic protein, is incorporated as a key biochemical outcome, measured from venous blood samples obtained in conjunction with routine clinical draws to enable minimally invasive longitudinal monitoring. The study aims not only to explore NfL as a prognostic indicator of long-term neurological outcome but also as a dynamic marker of treatment impact, hypothesizing that responders will show reductions in serum NfL consistent with attenuated ongoing axonal injury.

Neurophysiological recording protocols are designed to capture both spontaneous and stimulus-locked brain activity as correlates of consciousness and plasticity. EEG and high-density EEG acquisitions are typically performed at the bedside under standardized environmental conditions (moderated lighting, potential use of eye masks to reduce artefacts), and processing pipelines include channel-wise normalization, high-pass filtering to remove slow artefacts such as respiration, and low-pass filtering to suppress high-frequency noise. Beyond conventional spectral analyses, the study focuses on event-related potentials derived from paradigms such as auditory oddball stimulation, in which infrequent deviant sounds interspersed among frequent standard tones elicit P300 responses that have been shown to differentiate between diagnostic subgroups and may index residual conscious processing of salient stimuli, including responses to one's own name.

Autonomic and oculomotor measures complement EEG as additional windows onto arousal and information processing. Cardiac monitoring yields indices such as heart rate and heart rate variability, which can reflect autonomic balance and reactivity, while skin conductance responses quantify sympathetic activation in response to sensory events. Eye-tracking metrics captured through AAC devices include fixation duration and count, saccadic latency, amplitude and velocity, gaze accuracy, and distributions across pre-defined areas of interest, enabling fine-grained characterization of visual exploration and potential signs of goal-directed attention or command following in patients with severely limited motor output.